Presenting: Sylvania 7963 subminiature frame grid double triode
Shown next to a 6N23P for scale
From: http://rockgrotto.proboards.com/thread/9798/sylvania-7963-best-e88cc-planet?page=1&scrollTo=134293
"The 7963..... can trace its ancestry to the 6DJ8 family. In fact, with regard to audio applications, the 7963 offers performance in low level audio applications that is superior to all 6DJ8 variants, and to all other subminiature twin triodes as well."
The easiest way to use this tube in the Lyr is to solder the wire leads into the corresponding pin-holes of a 9-pin socket saver. Check the Rock Grotto thread for more info, but certainly not at all difficult for anyone comfortable with a soldering iron.
They can be purchased for about $25 on eBay, so not expensive. I have tested this tube in another amp, and while I do not have a lot of ear time with it, I do believe it is good enough and cheap enough to be well worth trying in the Lyr.
Cheers